[PATCH] Makefile: fix host CPP pollution in cmd_gen_envp

[Levi Shafter]

Commit 2956a84 ("Makefile: don't use CFLAGS for environment text file")
switched cmd_gen_envp to use $(cpp_flags) so that KCPPFLAGS would be
honored when preprocessing the environment text file. However,
cpp_flags also includes $(PLATFORM_CPPFLAGS), which carries
architecture-specific flags such as -march=armv8-a+crc set by
arch/arm/Makefile for CONFIG_ARM64_CRC32=y targets. These flags are
appropriate for cross-compiled object files but cause the host CPP
invocation to fail on x86 build machines:

  cc1: error: bad value ('armv8-a+crc') for '-march=' switch

KBUILD_CPPFLAGS already accumulates the user-supplied KCPPFLAGS via
"KBUILD_CPPFLAGS += $(KCPPFLAGS)", providing the behaviour 2956a84
intended without pulling in target architecture flags. Use it directly.

Fixes: 2956a84 ("Makefile: don't use CFLAGS for environment text file")
Reported-by: Levi Shafter <levi.shafter at elder-tomes.com>
Signed-off-by: Levi Shafter <levi.shafter at elder-tomes.com>
---
Sponsor: 21SoftWare LLC

 Makefile | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index dfc95d314dd..e2b8e6a1915 100644
--- a/Makefile
+++ b/Makefile
@@ -2147,7 +2147,8 @@ ENV_FILE := $(if
$(ENV_SOURCE_FILE),$(ENV_FILE_CFG),$(wildcard $(ENV_FILE_BOARD)
 quiet_cmd_gen_envp = ENVP    $@
       cmd_gen_envp = \
 	if [ -s "$(ENV_FILE)" ]; then \
-		$(CPP) -P $(cpp_flags) -x assembler-with-cpp -undef \
+		$(CPP) -P $(KBUILD_CPPFLAGS) $(UBOOTINCLUDE) \
+			-x assembler-with-cpp -undef \
 			-D__ASSEMBLY__ \
 			-D__UBOOT_CONFIG__ \
 			-DDEFAULT_DEVICE_TREE=$(subst ",,$(CONFIG_DEFAULT_DEVICE_TREE)) \